Vehicle stop lights are commonly tungsten filament lamps positioned in a reflector, and behind a red lens. The reflector directs all or most of the light through the lens, where only the red portion of the light is transmitted. Filtering inherently reduces the energy efficiency of the design. The typical taillamp, shows a hot spot where the white lamp overpowers the red filter. Away from the hot spot, the light appears less white or yellow, and becomes redder, but at the same time becomes less intense. The typical vehicle stop lamp then varies across its face in color and intensity. These variations are felt to be unesthetic by vehicle designers. There is then a general need for an efficient vehicle stop lamp, and a specific need for a vehicle stop lamp with an even distribution of color and intensity.
Neon lamps are known to produce red light, and therefore offer the opportunity of an unfiltered vehicle stop lamp. There are however problems to be overcome. Typical neon sign lamps use long tubes about one or two centimeters in diameter, that contain the diffused gaseous neon plasma light source. These lamps typically have inputs from 1100 to 1200 volts, at a few milliamps of power. These lamps give off a diffuse, low intensity light that has a chromaticity that does not meet automotive standards. For proper visibility, the light must be reflected and focused to concentrated it down the road, but a diffuse light source with a diameter one fir two centimeters cannot be efficiently reflected or focused. There is then a need for a small diameter, high intensity, neon stop lamp.
Narrow tube neon lamps are known. These lamps may have tube diameters of several millimeters, and have small electrodes providing very low output wattages. These lamps are used in artistic signs meant to be viewed at only a few feet. The small diameter tubes do not produce enough light to be sufficiently visible for vehicle use. Alternatively, a narrow central tube can be connected to broad end sections enclosing heavy electrodes. The larger electrodes provide increased power, without undue electrode erosion, but the large electrodes form large dark spots at each lamp end. The large, and dark electrode ends are felt to be unesthetic by vehicle designers.
The SAE has determined a particular red that is preferred for stop and warning illumination. Typical neon sign lamps are too orange to satisfy the SAE requirement, so there is a need for a neon lamp whose color meets the SAE chromaticity requirements. Typical neon lamps include mercury to simplify starting, but mercury based lamps do not start easily in cold environments. There is then a need for a mercury free neon lamp that meets SAE color requirements.
Examples of the prior art are shown in the following U.S. patents:
U.S. Pat. No. 2,123,709, issued to L. J. Bristow et al on Jul. 12, 1938 for a Therapeutic Light Ray Apparatus shows narrow, folded over neon tube for therapeutically probing body cavities.
U.S. Pat. No. 2,874,324, issued to G. F. Klepp et al on Feb. 17, 1959 for Electric Gaseous Discharge Tubes shows a neon discharge device having a pressure of about 25 millimeters of mercury. By choosing the envelope size and lamp pressure, the voltage regulation of the device can be optimized to offset temperature induced response variations in the device.
U.S. Pat. No. 4,792,727, issued to Valery A. Godyak on Dec. 20, 1988 for a System and Method for Operating a Discharge Lamp to Obtain Positive Volt-Ampere Characteristic shows a gas discharge lamp operated with a base electron heating current, and an additional pulsed ionization current occurring faster than the diffusion time of the gas, said to be typically about 1 microsecond. A driving wave with a frequency of 3333 Hertz and a pulse width of 1 microsecond is suggested. A lamp is operated at 264 milliamps.
U.S. Pat. No. 5,072,155, issued to Takehiko Sakurai et al. on Dec. 10, 1992 for Rare Gas Discharge Fluorescent Lamp Device discloses a copying machine lamp with high brightness and efficiency. Sakuria suggests in a xenon, argon, or krypton gas filled lamp, the use of a pulsed power supply wherein the pulse period is less than 150 microseconds, and the cycle period is greater than 5% of the pulse to avoid sputtering deterioration of the electrodes, and less than 70% of the pulse period to maximize light output for energy input. The gases discharge ultraviolet light that stimulates a fluorescent coating to produce visible light.